Asexual vs. Sexual Reproduction

Part 2 of 3

Sexual Reproduction

Sexual Reproduction

1. 2 parents 2. Sex cells: sperm and

egg 3. Sperm and egg join=

fertilization 4. Offspring look different

from parent (mixed DNA)

Sexual Reproduction

Sexual Reproduction

Examples– Humans, some plants,

mammals, fish, reptiles, etc.

Read:Sexual Reproduction: Gametes, External/Internal Fertilization, Male/Female

Sexual Reproduction

Sexual Reproduction in Animals

• involves specialized sex cells called gametes• the union of a male and female gamete results in

the formation of a zygote that develops into a new individual

Sexual Reproduction in

Plants

(Pistil)

Male Parts

Female Parts

pollen (male) + ovule (female) → single-celled zygote → multi-celled embryo (contained in a seed) → new individual

Sexual Reproduction in Plants• The stamen is the male part and contains

pollen • The carpels or pistil is the female part

and contains the ovule (eggs) • Pollen grains from the anther are

transferred to the stigma by the process of pollination– self pollination (plant pollinates its own eggs)– Assisted Pollination of a Flower (1:11)

– cross pollination (pollen from one plant pollinates another plants eggs)

Pollination• Flowers are designed (bright colors, stripes,

sweet smell, food) to attract insects to help with the pollination process– also wind, animals, birds can transport pollen

Plant Reproduction (1:30)

Plant Reproduction: Methods of Pollination (3:58)

Sexual Reproduction Summary

Male Gamete

Female Gamete

Type of Union

Result of Union

Final Result

Plants pollen ovule (egg)

pollination single cell zygote

multi-cell embryo

(in seed)

Animals sperm egg fertilization single cell zygote

multi-cell embryo

Asexual vs. sexual reproductionOrganisms that reproduce through asexual reproduction tend to grow in number exponentially. However, because they rely on mutation for variations in their DNA, all members of the species have similar vulnerabilities. Organisms that reproduce sexually yield a smaller number of offspring, but the large amount of variation in their genes makes them less susceptible to disease.Many organisms can reproduce sexually as well as asexually. Aphids, slime molds, sea anemones, some species of starfish (by fragmentation), and many plants are examples. When environmental factors are favorable, asexual reproduction is employed to exploit suitable conditions for survival such as an abundant food supply, adequate shelter, favorable climate, disease, optimum pH or a proper mix of other lifestyle requirements. Populations of these organisms increase exponentially via asexual reproductive strategies to take full advantage of the rich supply resources.When food sources have been depleted, the climate becomes hostile, or individual survival is jeopardized by some other adverse change in living conditions, these organisms switch to sexual forms of reproduction. Sexual reproduction ensures a mixing of the gene pool of the species. The variations found in offspring of sexual reproduction allow some individuals to be better suited for survival and provide a mechanism for selective adaptation to occur. In addition, sexual reproduction usually results in the formation of a life stage that is able to endure the conditions that threaten the offspring of an asexual parent. Thus, seeds, spores, eggs, pupae, cysts or other "over-wintering" stages of sexual reproduction ensure the survival during unfavorable times and the organism can "wait out" adverse situations until a swing back to suitability occurs.

Some Organisms do Both• Most plants that produce seeds (sexual

reproduction) can also reproduce asexually by things like cuttings or runners

• This gives them an advantage for survival sponges and hydra mosses onions

Asexual and Sexual Reproduction - I can do both!

Aphids

Asexual and Sexual Reproduction - I can do both!

Fuligo septica, the "dog vomit" slime mold

Slime mold (Physarum polycephalum)

Slime mold growing out of a bin of wet paper

Mycetozoa from Ernst Haeckel's 1904 Kunstformen der Natur (Artforms of Nature)

Mycetozoa is a grouping of slime molds. Sea anemone

Asexual Reproduction – Grade Six

9

Attachment E Asexual Reproduction Resource Page

Any of the following could be used in the science lab to reinforce content.

Organism Type of Asexual Reproduction

Description

Whiptail lizards

Parthenogenesis A female whiptail lizard may produce eggs that develop into genetically identical versions of itself. In some species, there are entire clonal populations of this lizard. Most whiptail lizard species do reproduce sexually, though.

Bacteria

Fission A single-celled organism that has no nuclei or cell walls and reproduce by splitting in two.

Spider plant Vegetative Propagation

Spider plants reproduce new plants by the division of cells from roots or runners. These can be placed in water or soil to produce another plant. Spider plants also reproduce sexually.

Strawberries

Vegetative Propagation

Strawberries reproduce new plants by the division of cells from runners or roots. Strawberries also reproduce sexually.

Some flatworms

Fragmentation Some flatworms can grow by cell division from a fragmented section of its body.

Paramecium

Fission Paramecium is a single-celled organism that reproduces by splitting in two.

Mint

Vegetative Propagation

Division of the roots reproduces new mint. Mint also reproduces sexually.

Blue-green algae

Fission A single celled organism that reproduces by splitting in two.

Protists Fission Protists have a nucleus and are therefore eukaryotic. Some protists contain chloroplasts and make their own food, and others don't. But all reproduce by fission-the process of splitting in two.

Hydra

Budding Cell division forms a bud that is an identical copy of its single parent that separates from the parent and becomes independent.

Organisms and Types of Asexual Reproduction

Which is Better?It depends!

Asexual Reproduction• advantages

– does not require special cells or a lot of energy

– can produce offspring quickly

– in a stable environment creates large, thriving population

• disadvantages– limited ability to adapt– face massive die-off if

environment changes

Sexual Reproduction• advantages

– lots of variation within a species

– able to live in a variety of environmental settings

– able to adapt to changes in the environment

• disadvantages– needs time & energy– produce small

populations